import {
  AnimationClip,
  Bone,
  Box3,
  BufferAttribute,
  BufferGeometry,
  CanvasTexture,
  ClampToEdgeWrapping,
  Color,
  DirectionalLight,
  DoubleSide,
  FileLoader,
  FrontSide,
  Group,
  ImageBitmapLoader,
  InterleavedBuffer,
  InterleavedBufferAttribute,
  Interpolant,
  InterpolateDiscrete,
  InterpolateLinear,
  Line,
  LineBasicMaterial,
  LineLoop,
  LineSegments,
  LinearFilter,
  LinearMipmapLinearFilter,
  LinearMipmapNearestFilter,
  Loader,
  LoaderUtils,
  Material,
  MathUtils,
  Matrix4,
  Mesh,
  MeshBasicMaterial,
  MeshPhysicalMaterial,
  MeshStandardMaterial,
  MirroredRepeatWrapping,
  NearestFilter,
  NearestMipmapLinearFilter,
  NearestMipmapNearestFilter,
  NumberKeyframeTrack,
  Object3D,
  OrthographicCamera,
  PerspectiveCamera,
  PointLight,
  Points,
  PointsMaterial,
  PropertyBinding,
  QuaternionKeyframeTrack,
  RGBFormat,
  RepeatWrapping,
  Skeleton,
  SkinnedMesh,
  Sphere,
  SpotLight,
  TangentSpaceNormalMap,
  TextureLoader,
  TriangleFanDrawMode,
  TriangleStripDrawMode,
  Vector2,
  Vector3,
  VectorKeyframeTrack,
  sRGBEncoding
} from 'three';
global.XMLHttpRequest = require('xmlhttprequest').XMLHttpRequest;
global.Blob = require("cross-blob");
global.blobUtil = require("blob-util");

var GLTFLoader = ( function () {

  function GLTFLoader( manager ) {

    Loader.call( this, manager );

    this.dracoLoader = null;
    this.ddsLoader = null;
    this.ktx2Loader = null;

    this.pluginCallbacks = [];

    this.register( function ( parser ) {

      return new GLTFMaterialsClearcoatExtension( parser );

    } );
    this.register( function ( parser ) {

      return new GLTFTextureBasisUExtension( parser );

    } );

    this.register( function ( parser ) {

      return new GLTFMaterialsTransmissionExtension( parser );

    } );

  }

  GLTFLoader.prototype = Object.assign( Object.create( Loader.prototype ), {

    constructor: GLTFLoader,

    load: function ( url, onLoad, onProgress, onError ) {

      var scope = this;

      var resourcePath;

      if ( this.resourcePath !== '' ) {

        resourcePath = this.resourcePath;

      } else if ( this.path !== '' ) {

        resourcePath = this.path;

      } else {

        resourcePath = LoaderUtils.extractUrlBase( url );

      }

      // Tells the LoadingManager to track an extra item, which resolves after
      // the model is fully loaded. This means the count of items loaded will
      // be incorrect, but ensures manager.onLoad() does not fire early.
      scope.manager.itemStart( url );

      var _onError = function ( e ) {

        if ( onError ) {

          onError( e );

        } else {

          console.error( e );

        }

        scope.manager.itemError( url );
        scope.manager.itemEnd( url );

      };

      var loader = new FileLoader( scope.manager );

      loader.setPath( this.path );
      loader.setResponseType( 'arraybuffer' );
      loader.setRequestHeader( this.requestHeader );

      if ( scope.crossOrigin === 'use-credentials' ) {

        loader.setWithCredentials( true );

      }

      loader.load( url, function ( data ) {

        try {

          scope.parse( data, resourcePath, function ( gltf ) {

            onLoad( gltf );

            scope.manager.itemEnd( url );

          }, _onError );

        } catch ( e ) {

          _onError( e );

        }

      }, onProgress, _onError );

    },

    setDRACOLoader: function ( dracoLoader ) {

      this.dracoLoader = dracoLoader;
      return this;

    },

    setDDSLoader: function ( ddsLoader ) {

      this.ddsLoader = ddsLoader;
      return this;

    },

    setKTX2Loader: function ( ktx2Loader ) {

      this.ktx2Loader = ktx2Loader;
      return this;

    },

    register: function ( callback ) {

      if ( this.pluginCallbacks.indexOf( callback ) === - 1 ) {

        this.pluginCallbacks.push( callback );

      }

      return this;

    },

    unregister: function ( callback ) {

      if ( this.pluginCallbacks.indexOf( callback ) !== - 1 ) {

        this.pluginCallbacks.splice( this.pluginCallbacks.indexOf( callback ), 1 );

      }

      return this;

    },

    parse: function ( data, path, onLoad, onError ) {

      var content;
      var extensions = {};
      var plugins = {};

      if ( typeof data === 'string' ) {

        content = data;

      } else {

        var magic = LoaderUtils.decodeText( new Uint8Array( data, 0, 4 ) );

        if ( magic === BINARY_EXTENSION_HEADER_MAGIC ) {

          try {

            extensions[ EXTENSIONS.KHR_BINARY_GLTF ] = new GLTFBinaryExtension( data );

          } catch ( error ) {

            if ( onError ) onError( error );
            return;

          }

          content = extensions[ EXTENSIONS.KHR_BINARY_GLTF ].content;

        } else {

          content = LoaderUtils.decodeText( new Uint8Array( data ) );

        }

      }

      var json = JSON.parse( content );

      if ( json.asset === undefined || json.asset.version[ 0 ] < 2 ) {

        if ( onError ) onError( new Error( 'THREE.GLTFLoader: Unsupported asset. glTF versions >=2.0 are supported.' ) );
        return;

      }

      var parser = new GLTFParser( json, {

        path: path || this.resourcePath || '',
        crossOrigin: this.crossOrigin,
        manager: this.manager,
        ktx2Loader: this.ktx2Loader

      } );

      parser.fileLoader.setRequestHeader( this.requestHeader );

      for ( var i = 0; i < this.pluginCallbacks.length; i ++ ) {

        var plugin = this.pluginCallbacks[ i ]( parser );
        plugins[ plugin.name ] = plugin;

        // Workaround to avoid determining as unknown extension
        // in addUnknownExtensionsToUserData().
        // Remove this workaround if we move all the existing
        // extension handlers to plugin system
        extensions[ plugin.name ] = true;

      }

      if ( json.extensionsUsed ) {

        for ( var i = 0; i < json.extensionsUsed.length; ++ i ) {

          var extensionName = json.extensionsUsed[ i ];
          var extensionsRequired = json.extensionsRequired || [];

          switch ( extensionName ) {

            case EXTENSIONS.KHR_LIGHTS_PUNCTUAL:
              extensions[ extensionName ] = new GLTFLightsExtension( json );
              break;

            case EXTENSIONS.KHR_MATERIALS_UNLIT:
              extensions[ extensionName ] = new GLTFMaterialsUnlitExtension();
              break;

            case EXTENSIONS.KHR_MATERIALS_PBR_SPECULAR_GLOSSINESS:
              extensions[ extensionName ] = new GLTFMaterialsPbrSpecularGlossinessExtension();
              break;

            case EXTENSIONS.KHR_DRACO_MESH_COMPRESSION:
              extensions[ extensionName ] = new GLTFDracoMeshCompressionExtension( json, this.dracoLoader );
              break;

            case EXTENSIONS.MSFT_TEXTURE_DDS:
              extensions[ extensionName ] = new GLTFTextureDDSExtension( this.ddsLoader );
              break;

            case EXTENSIONS.KHR_TEXTURE_TRANSFORM:
              extensions[ extensionName ] = new GLTFTextureTransformExtension();
              break;

            case EXTENSIONS.KHR_MESH_QUANTIZATION:
              extensions[ extensionName ] = new GLTFMeshQuantizationExtension();
              break;

            default:

              if ( extensionsRequired.indexOf( extensionName ) >= 0 && plugins[ extensionName ] === undefined ) {

                console.warn( `THREE.GLTFLoader: Unknown extension ${extensionName}.` );

              }

          }

        }

      }

      parser.setExtensions( extensions );
      parser.setPlugins( plugins );
      parser.parse( onLoad, onError );

    }

  } );

  /* GLTFREGISTRY */

  function GLTFRegistry() {

    var objects = {};

    return  {

      get: function ( key ) {

        return objects[ key ];

      },

      add: function ( key, object ) {

        objects[ key ] = object;

      },

      remove: function ( key ) {

        delete objects[ key ];

      },

      removeAll: function () {

        objects = {};

      }

    };

  }

  /*********************************/
  /********** EXTENSIONS ***********/
  /*********************************/

  var EXTENSIONS = {
    KHR_BINARY_GLTF: 'KHR_binary_glTF',
    KHR_DRACO_MESH_COMPRESSION: 'KHR_draco_mesh_compression',
    KHR_LIGHTS_PUNCTUAL: 'KHR_lights_punctual',
    KHR_MATERIALS_CLEARCOAT: 'KHR_materials_clearcoat',
    KHR_MATERIALS_PBR_SPECULAR_GLOSSINESS: 'KHR_materials_pbrSpecularGlossiness',
    KHR_MATERIALS_TRANSMISSION: 'KHR_materials_transmission',
    KHR_MATERIALS_UNLIT: 'KHR_materials_unlit',
    KHR_TEXTURE_BASISU: 'KHR_texture_basisu',
    KHR_TEXTURE_TRANSFORM: 'KHR_texture_transform',
    KHR_MESH_QUANTIZATION: 'KHR_mesh_quantization',
    MSFT_TEXTURE_DDS: 'MSFT_texture_dds'
  };

  /**
   * DDS Texture Extension
   *
   * Specification: https://github.com/KhronosGroup/glTF/tree/master/extensions/2.0/Vendor/MSFT_texture_dds
   *
   */
  function GLTFTextureDDSExtension( ddsLoader ) {

    if ( ! ddsLoader ) {

      throw new Error( 'THREE.GLTFLoader: Attempting to load .dds texture without importing DDSLoader' );

    }

    this.name = EXTENSIONS.MSFT_TEXTURE_DDS;
    this.ddsLoader = ddsLoader;

  }

  /**
   * Punctual Lights Extension
   *
   * Specification: https://github.com/KhronosGroup/glTF/tree/master/extensions/2.0/Khronos/KHR_lights_punctual
   */
  function GLTFLightsExtension( json ) {

    this.name = EXTENSIONS.KHR_LIGHTS_PUNCTUAL;

    var extension = ( json.extensions && json.extensions[ EXTENSIONS.KHR_LIGHTS_PUNCTUAL ] ) || {};
    this.lightDefs = extension.lights || [];

  }

  GLTFLightsExtension.prototype.loadLight = function ( lightIndex ) {

    var lightDef = this.lightDefs[ lightIndex ];
    var lightNode;

    var color = new Color( 0xffffff );
    if ( lightDef.color !== undefined ) color.fromArray( lightDef.color );

    var range = lightDef.range !== undefined ? lightDef.range : 0;

    switch ( lightDef.type ) {

      case 'directional':
        lightNode = new DirectionalLight( color );
        lightNode.target.position.set( 0, 0, - 1 );
        lightNode.add( lightNode.target );
        break;

      case 'point':
        lightNode = new PointLight( color );
        lightNode.distance = range;
        break;

      case 'spot':
        lightNode = new SpotLight( color );
        lightNode.distance = range;
        // Handle spotlight properties.
        lightDef.spot = lightDef.spot || {};
        lightDef.spot.innerConeAngle = lightDef.spot.innerConeAngle !== undefined ? lightDef.spot.innerConeAngle : 0;
        lightDef.spot.outerConeAngle = lightDef.spot.outerConeAngle !== undefined ? lightDef.spot.outerConeAngle : Math.PI / 4.0;
        lightNode.angle = lightDef.spot.outerConeAngle;
        lightNode.penumbra = 1.0 - lightDef.spot.innerConeAngle / lightDef.spot.outerConeAngle;
        lightNode.target.position.set( 0, 0, - 1 );
        lightNode.add( lightNode.target );
        break;

      default:
        throw new Error( 'THREE.GLTFLoader: Unexpected light type, ' + lightDef.type + '.' );

    }

    // Some lights (e.g. spot) default to a position other than the origin. Reset the position
    // here, because node-level parsing will only override position if explicitly specified.
    lightNode.position.set( 0, 0, 0 );

    lightNode.decay = 2;

    if ( lightDef.intensity !== undefined ) lightNode.intensity = lightDef.intensity;

    lightNode.name = lightDef.name || ( 'light_' + lightIndex );

    return Promise.resolve( lightNode );

  };

  /**
   * Unlit Materials Extension
   *
   * Specification: https://github.com/KhronosGroup/glTF/tree/master/extensions/2.0/Khronos/KHR_materials_unlit
   */
  function GLTFMaterialsUnlitExtension() {

    this.name = EXTENSIONS.KHR_MATERIALS_UNLIT;

  }

  GLTFMaterialsUnlitExtension.prototype.getMaterialType = function () {

    return MeshBasicMaterial;

  };

  GLTFMaterialsUnlitExtension.prototype.extendParams = function ( materialParams, materialDef, parser ) {

    var pending = [];

    materialParams.color = new Color( 1.0, 1.0, 1.0 );
    materialParams.opacity = 1.0;

    var metallicRoughness = materialDef.pbrMetallicRoughness;

    if ( metallicRoughness ) {

      if ( Array.isArray( metallicRoughness.baseColorFactor ) ) {

        var array = metallicRoughness.baseColorFactor;

        materialParams.color.fromArray( array );
        materialParams.opacity = array[ 3 ];

      }

      if ( metallicRoughness.baseColorTexture !== undefined ) {

        pending.push( parser.assignTexture( materialParams, 'map', metallicRoughness.baseColorTexture ) );

      }

    }

    return Promise.all( pending );

  };

  /**
   * Clearcoat Materials Extension
   *
   * Specification: https://github.com/KhronosGroup/glTF/tree/master/extensions/2.0/Khronos/KHR_materials_clearcoat
   */
  function GLTFMaterialsClearcoatExtension( parser ) {

    this.parser = parser;
    this.name = EXTENSIONS.KHR_MATERIALS_CLEARCOAT;

  }

  GLTFMaterialsClearcoatExtension.prototype.getMaterialType = function ( materialIndex ) {

    var parser = this.parser;
    var materialDef = parser.json.materials[ materialIndex ];

    if ( ! materialDef.extensions || ! materialDef.extensions[ this.name ] ) return null;

    return MeshPhysicalMaterial;

  };

  GLTFMaterialsClearcoatExtension.prototype.extendMaterialParams = function ( materialIndex, materialParams ) {

    var parser = this.parser;
    var materialDef = parser.json.materials[ materialIndex ];

    if ( ! materialDef.extensions || ! materialDef.extensions[ this.name ] ) {

      return Promise.resolve();

    }

    var pending = [];

    var extension = materialDef.extensions[ this.name ];

    if ( extension.clearcoatFactor !== undefined ) {

      materialParams.clearcoat = extension.clearcoatFactor;

    }

    if ( extension.clearcoatTexture !== undefined ) {

      pending.push( parser.assignTexture( materialParams, 'clearcoatMap', extension.clearcoatTexture ) );

    }

    if ( extension.clearcoatRoughnessFactor !== undefined ) {

      materialParams.clearcoatRoughness = extension.clearcoatRoughnessFactor;

    }

    if ( extension.clearcoatRoughnessTexture !== undefined ) {

      pending.push( parser.assignTexture( materialParams, 'clearcoatRoughnessMap', extension.clearcoatRoughnessTexture ) );

    }

    if ( extension.clearcoatNormalTexture !== undefined ) {

      pending.push( parser.assignTexture( materialParams, 'clearcoatNormalMap', extension.clearcoatNormalTexture ) );

      if ( extension.clearcoatNormalTexture.scale !== undefined ) {

        var scale = extension.clearcoatNormalTexture.scale;

        materialParams.clearcoatNormalScale = new Vector2( scale, scale );

      }

    }

    return Promise.all( pending );

  };

  /**
   * Transmission Materials Extension
   *
   * Specification: https://github.com/KhronosGroup/glTF/tree/master/extensions/2.0/Khronos/KHR_materials_transmission
   * Draft: https://github.com/KhronosGroup/glTF/pull/1698
   */
  function GLTFMaterialsTransmissionExtension( parser ) {

    this.parser = parser;
    this.name = EXTENSIONS.KHR_MATERIALS_TRANSMISSION;

  }

  GLTFMaterialsTransmissionExtension.prototype.getMaterialType = function ( materialIndex ) {

    var parser = this.parser;
    var materialDef = parser.json.materials[ materialIndex ];

    if ( ! materialDef.extensions || ! materialDef.extensions[ this.name ] ) return null;

    return MeshPhysicalMaterial;

  };

  GLTFMaterialsTransmissionExtension.prototype.extendMaterialParams = function ( materialIndex, materialParams ) {

    var parser = this.parser;
    var materialDef = parser.json.materials[ materialIndex ];

    if ( ! materialDef.extensions || ! materialDef.extensions[ this.name ] ) {

      return Promise.resolve();

    }

    var pending = [];

    var extension = materialDef.extensions[ this.name ];

    if ( extension.transmissionFactor !== undefined ) {

      materialParams.transmission = extension.transmissionFactor;

    }

    if ( extension.transmissionTexture !== undefined ) {

      pending.push( parser.assignTexture( materialParams, 'transmissionMap', extension.transmissionTexture ) );

    }

    return Promise.all( pending );

  };

  /**
   * BasisU Texture Extension
   *
   * Specification: https://github.com/KhronosGroup/glTF/tree/master/extensions/2.0/Khronos/KHR_texture_basisu
   * (draft PR https://github.com/KhronosGroup/glTF/pull/1751)
   */
  function GLTFTextureBasisUExtension( parser ) {

    this.parser = parser;
    this.name = EXTENSIONS.KHR_TEXTURE_BASISU;

  }

  /* BINARY EXTENSION */
  var BINARY_EXTENSION_HEADER_MAGIC = 'glTF';
  var BINARY_EXTENSION_HEADER_LENGTH = 12;
  var BINARY_EXTENSION_CHUNK_TYPES = { JSON: 0x4E4F534A, BIN: 0x004E4942 };

  function GLTFBinaryExtension( data ) {

    this.name = EXTENSIONS.KHR_BINARY_GLTF;
    this.content = null;
    this.body = null;

    var headerView = new DataView( data, 0, BINARY_EXTENSION_HEADER_LENGTH );

    this.header = {
      magic: LoaderUtils.decodeText( new Uint8Array( data.slice( 0, 4 ) ) ),
      version: headerView.getUint32( 4, true ),
      length: headerView.getUint32( 8, true )
    };

    if ( this.header.magic !== BINARY_EXTENSION_HEADER_MAGIC ) {

      throw new Error( 'THREE.GLTFLoader: Unsupported glTF-Binary header.' );

    } else if ( this.header.version < 2.0 ) {

      throw new Error( 'THREE.GLTFLoader: Legacy binary file detected.' );

    }

    var chunkView = new DataView( data, BINARY_EXTENSION_HEADER_LENGTH );
    var chunkIndex = 0;

    while ( chunkIndex < chunkView.byteLength ) {

      var chunkLength = chunkView.getUint32( chunkIndex, true );
      chunkIndex += 4;

      var chunkType = chunkView.getUint32( chunkIndex, true );
      chunkIndex += 4;

      if ( chunkType === BINARY_EXTENSION_CHUNK_TYPES.JSON ) {

        var contentArray = new Uint8Array( data, BINARY_EXTENSION_HEADER_LENGTH + chunkIndex, chunkLength );
        this.content = LoaderUtils.decodeText( contentArray );

      } else if ( chunkType === BINARY_EXTENSION_CHUNK_TYPES.BIN ) {

        var byteOffset = BINARY_EXTENSION_HEADER_LENGTH + chunkIndex;
        this.body = data.slice( byteOffset, byteOffset + chunkLength );

      }

      // Clients must ignore chunks with unknown types.

      chunkIndex += chunkLength;

    }

    if ( this.content === null ) {

      throw new Error( 'THREE.GLTFLoader: JSON content not found.' );

    }

  }

  /**
   * DRACO Mesh Compression Extension
   *
   * Specification: https://github.com/KhronosGroup/glTF/tree/master/extensions/2.0/Khronos/KHR_draco_mesh_compression
   */
  function GLTFDracoMeshCompressionExtension( json, dracoLoader ) {

    if ( ! dracoLoader ) {

      throw new Error( 'THREE.GLTFLoader: No DRACOLoader instance provided.' );

    }

    this.name = EXTENSIONS.KHR_DRACO_MESH_COMPRESSION;
    this.json = json;
    this.dracoLoader = dracoLoader;
    this.dracoLoader.preload();

  }

  GLTFDracoMeshCompressionExtension.prototype.decodePrimitive = function ( primitive, parser ) {

    var json = this.json;
    var dracoLoader = this.dracoLoader;
    var bufferViewIndex = primitive.extensions[ this.name ].bufferView;
    var gltfAttributeMap = primitive.extensions[ this.name ].attributes;
    var threeAttributeMap = {};
    var attributeNormalizedMap = {};
    var attributeTypeMap = {};

    for ( var attributeName in gltfAttributeMap ) {

      var threeAttributeName = ATTRIBUTES[ attributeName ] || attributeName.toLowerCase();

      threeAttributeMap[ threeAttributeName ] = gltfAttributeMap[ attributeName ];

    }

    for ( attributeName in primitive.attributes ) {

      var threeAttributeName = ATTRIBUTES[ attributeName ] || attributeName.toLowerCase();

      if ( gltfAttributeMap[ attributeName ] !== undefined ) {

        var accessorDef = json.accessors[ primitive.attributes[ attributeName ] ];
        var componentType = WEBGL_COMPONENT_TYPES[ accessorDef.componentType ];

        attributeTypeMap[ threeAttributeName ] = componentType;
        attributeNormalizedMap[ threeAttributeName ] = accessorDef.normalized === true;

      }

    }

    return parser.getDependency( 'bufferView', bufferViewIndex ).then( function ( bufferView ) {

      return new Promise( function ( resolve ) {

        dracoLoader.decodeDracoFile( bufferView, function ( geometry ) {

          for ( var attributeName in geometry.attributes ) {

            var attribute = geometry.attributes[ attributeName ];
            var normalized = attributeNormalizedMap[ attributeName ];

            if ( normalized !== undefined ) attribute.normalized = normalized;

          }

          resolve( geometry );

        }, threeAttributeMap, attributeTypeMap );

      } );

    } );

  };

  /**
   * Texture Transform Extension
   *
   * Specification: https://github.com/KhronosGroup/glTF/tree/master/extensions/2.0/Khronos/KHR_texture_transform
   */
  function GLTFTextureTransformExtension() {

    this.name = EXTENSIONS.KHR_TEXTURE_TRANSFORM;

  }

  GLTFTextureTransformExtension.prototype.extendTexture = function ( texture, transform ) {

    texture = texture.clone();

    if ( transform.offset !== undefined ) {

      texture.offset.fromArray( transform.offset );

    }

    if ( transform.rotation !== undefined ) {

      texture.rotation = transform.rotation;

    }

    if ( transform.scale !== undefined ) {

      texture.repeat.fromArray( transform.scale );

    }

    if ( transform.texCoord !== undefined ) {

      console.warn( 'THREE.GLTFLoader: Custom UV sets in ' + this.name + ' extension not yet supported.' );

    }

    texture.needsUpdate = true;

    return texture;

  };

  /**
   * Specular-Glossiness Extension
   *
   * Specification: https://github.com/KhronosGroup/glTF/tree/master/extensions/2.0/Khronos/KHR_materials_pbrSpecularGlossiness
   */

  /**
   * A sub class of StandardMaterial with some of the functionality
   * changed via the `onBeforeCompile` callback
   * @pailhead
   */

  function GLTFMeshStandardSGMaterial( params ) {

    MeshStandardMaterial.call( this );

    this.isGLTFSpecularGlossinessMaterial = true;

    //various chunks that need replacing
    var specularMapParsFragmentChunk = [
      '#ifdef USE_SPECULARMAP',
      ' uniform sampler2D specularMap;',
      '#endif'
    ].join( '\n' );

    var glossinessMapParsFragmentChunk = [
      '#ifdef USE_GLOSSINESSMAP',
      ' uniform sampler2D glossinessMap;',
      '#endif'
    ].join( '\n' );

    var specularMapFragmentChunk = [
      'vec3 specularFactor = specular;',
      '#ifdef USE_SPECULARMAP',
      ' vec4 texelSpecular = texture2D( specularMap, vUv );',
      ' texelSpecular = sRGBToLinear( texelSpecular );',
      ' // reads channel RGB, compatible with a glTF Specular-Glossiness (RGBA) texture',
      ' specularFactor *= texelSpecular.rgb;',
      '#endif'
    ].join( '\n' );

    var glossinessMapFragmentChunk = [
      'float glossinessFactor = glossiness;',
      '#ifdef USE_GLOSSINESSMAP',
      ' vec4 texelGlossiness = texture2D( glossinessMap, vUv );',
      ' // reads channel A, compatible with a glTF Specular-Glossiness (RGBA) texture',
      ' glossinessFactor *= texelGlossiness.a;',
      '#endif'
    ].join( '\n' );

    var lightPhysicalFragmentChunk = [
      'PhysicalMaterial material;',
      'material.diffuseColor = diffuseColor.rgb;',
      'vec3 dxy = max( abs( dFdx( geometryNormal ) ), abs( dFdy( geometryNormal ) ) );',
      'float geometryRoughness = max( max( dxy.x, dxy.y ), dxy.z );',
      'material.specularRoughness = max( 1.0 - glossinessFactor, 0.0525 );// 0.0525 corresponds to the base mip of a 256 cubemap.',
      'material.specularRoughness += geometryRoughness;',
      'material.specularRoughness = min( material.specularRoughness, 1.0 );',
      'material.specularColor = specularFactor.rgb;',
    ].join( '\n' );

    var uniforms = {
      specular: { value: new Color().setHex( 0xffffff ) },
      glossiness: { value: 1 },
      specularMap: { value: null },
      glossinessMap: { value: null }
    };

    this._extraUniforms = uniforms;

    // please see #14031 or #13198 for an alternate approach
    this.onBeforeCompile = function ( shader ) {

      for ( var uniformName in uniforms ) {

        shader.uniforms[ uniformName ] = uniforms[ uniformName ];

      }

      shader.fragmentShader = shader.fragmentShader.replace( 'uniform float roughness;', 'uniform vec3 specular;' );
      shader.fragmentShader = shader.fragmentShader.replace( 'uniform float metalness;', 'uniform float glossiness;' );
      shader.fragmentShader = shader.fragmentShader.replace( '#include <roughnessmap_pars_fragment>', specularMapParsFragmentChunk );
      shader.fragmentShader = shader.fragmentShader.replace( '#include <metalnessmap_pars_fragment>', glossinessMapParsFragmentChunk );
      shader.fragmentShader = shader.fragmentShader.replace( '#include <roughnessmap_fragment>', specularMapFragmentChunk );
      shader.fragmentShader = shader.fragmentShader.replace( '#include <metalnessmap_fragment>', glossinessMapFragmentChunk );
      shader.fragmentShader = shader.fragmentShader.replace( '#include <lights_physical_fragment>', lightPhysicalFragmentChunk );

    };

    /*eslint-disable*/
    Object.defineProperties(
      this,
      {
        specular: {
          get: function () { return uniforms.specular.value; },
          set: function ( v ) { uniforms.specular.value = v; }
        },
        specularMap: {
          get: function () { return uniforms.specularMap.value; },
          set: function ( v ) { uniforms.specularMap.value = v; }
        },
        glossiness: {
          get: function () { return uniforms.glossiness.value; },
          set: function ( v ) { uniforms.glossiness.value = v; }
        },
        glossinessMap: {
          get: function () { return uniforms.glossinessMap.value; },
          set: function ( v ) {

            uniforms.glossinessMap.value = v;
            //how about something like this - @pailhead
            if ( v ) {

              this.defines.USE_GLOSSINESSMAP = '';
              // set USE_ROUGHNESSMAP to enable vUv
              this.defines.USE_ROUGHNESSMAP = '';

            } else {

              delete this.defines.USE_ROUGHNESSMAP;
              delete this.defines.USE_GLOSSINESSMAP;

            }

          }
        }
      }
    );

    /*eslint-enable*/
    delete this.metalness;
    delete this.roughness;
    delete this.metalnessMap;
    delete this.roughnessMap;

    this.setValues( params );

  }

  GLTFMeshStandardSGMaterial.prototype = Object.create( MeshStandardMaterial.prototype );
  GLTFMeshStandardSGMaterial.prototype.constructor = GLTFMeshStandardSGMaterial;

  GLTFMeshStandardSGMaterial.prototype.copy = function ( source ) {

    MeshStandardMaterial.prototype.copy.call( this, source );
    this.specularMap = source.specularMap;
    this.specular.copy( source.specular );
    this.glossinessMap = source.glossinessMap;
    this.glossiness = source.glossiness;
    delete this.metalness;
    delete this.roughness;
    delete this.metalnessMap;
    delete this.roughnessMap;
    return this;

  };

  function GLTFMaterialsPbrSpecularGlossinessExtension() {

    return {

      name: EXTENSIONS.KHR_MATERIALS_PBR_SPECULAR_GLOSSINESS,

      specularGlossinessParams: [
        'color',
        'map',
        'lightMap',
        'lightMapIntensity',
        'aoMap',
        'aoMapIntensity',
        'emissive',
        'emissiveIntensity',
        'emissiveMap',
        'bumpMap',
        'bumpScale',
        'normalMap',
        'normalMapType',
        'displacementMap',
        'displacementScale',
        'displacementBias',
        'specularMap',
        'specular',
        'glossinessMap',
        'glossiness',
        'alphaMap',
        'envMap',
        'envMapIntensity',
        'refractionRatio',
      ],

      getMaterialType: function () {

        return GLTFMeshStandardSGMaterial;

      },

      extendParams: function ( materialParams, materialDef, parser ) {

        var pbrSpecularGlossiness = materialDef.extensions[ this.name ];

        materialParams.color = new Color( 1.0, 1.0, 1.0 );
        materialParams.opacity = 1.0;

        var pending = [];

        if ( Array.isArray( pbrSpecularGlossiness.diffuseFactor ) ) {

          var array = pbrSpecularGlossiness.diffuseFactor;

          materialParams.color.fromArray( array );
          materialParams.opacity = array[ 3 ];

        }

        if ( pbrSpecularGlossiness.diffuseTexture !== undefined ) {

          pending.push( parser.assignTexture( materialParams, 'map', pbrSpecularGlossiness.diffuseTexture ) );

        }

        materialParams.emissive = new Color( 0.0, 0.0, 0.0 );
        materialParams.glossiness = pbrSpecularGlossiness.glossinessFactor !== undefined ? pbrSpecularGlossiness.glossinessFactor : 1.0;
        materialParams.specular = new Color( 1.0, 1.0, 1.0 );

        if ( Array.isArray( pbrSpecularGlossiness.specularFactor ) ) {

          materialParams.specular.fromArray( pbrSpecularGlossiness.specularFactor );

        }

        if ( pbrSpecularGlossiness.specularGlossinessTexture !== undefined ) {

          var specGlossMapDef = pbrSpecularGlossiness.specularGlossinessTexture;
          pending.push( parser.assignTexture( materialParams, 'glossinessMap', specGlossMapDef ) );
          pending.push( parser.assignTexture( materialParams, 'specularMap', specGlossMapDef ) );

        }

        return Promise.all( pending );

      },

      createMaterial: function ( materialParams ) {

        var material = new GLTFMeshStandardSGMaterial( materialParams );
        material.fog = true;

        material.color = materialParams.color;

        material.map = materialParams.map === undefined ? null : materialParams.map;

        material.lightMap = null;
        material.lightMapIntensity = 1.0;

        material.aoMap = materialParams.aoMap === undefined ? null : materialParams.aoMap;
        material.aoMapIntensity = 1.0;

        material.emissive = materialParams.emissive;
        material.emissiveIntensity = 1.0;
        material.emissiveMap = materialParams.emissiveMap === undefined ? null : materialParams.emissiveMap;

        material.bumpMap = materialParams.bumpMap === undefined ? null : materialParams.bumpMap;
        material.bumpScale = 1;

        material.normalMap = materialParams.normalMap === undefined ? null : materialParams.normalMap;
        material.normalMapType = TangentSpaceNormalMap;

        if ( materialParams.normalScale ) material.normalScale = materialParams.normalScale;

        material.displacementMap = null;
        material.displacementScale = 1;
        material.displacementBias = 0;

        material.specularMap = materialParams.specularMap === undefined ? null : materialParams.specularMap;
        material.specular = materialParams.specular;

        material.glossinessMap = materialParams.glossinessMap === undefined ? null : materialParams.glossinessMap;
        material.glossiness = materialParams.glossiness;

        material.alphaMap = null;

        material.envMap = materialParams.envMap === undefined ? null : materialParams.envMap;
        material.envMapIntensity = 1.0;

        material.refractionRatio = 0.98;

        return material;

      },

    };

  }

  /**
   * Mesh Quantization Extension
   *
   * Specification: https://github.com/KhronosGroup/glTF/tree/master/extensions/2.0/Khronos/KHR_mesh_quantization
   */
  function GLTFMeshQuantizationExtension() {

    this.name = EXTENSIONS.KHR_MESH_QUANTIZATION;

  }

  /*********************************/
  /********** INTERPOLATION ********/
  /*********************************/

  // Spline Interpolation
  // Specification: https://github.com/KhronosGroup/glTF/blob/master/specification/2.0/README.md#appendix-c-spline-interpolation
  function GLTFCubicSplineInterpolant( parameterPositions, sampleValues, sampleSize, resultBuffer ) {

    Interpolant.call( this, parameterPositions, sampleValues, sampleSize, resultBuffer );

  }

  GLTFCubicSplineInterpolant.prototype = Object.create( Interpolant.prototype );
  GLTFCubicSplineInterpolant.prototype.constructor = GLTFCubicSplineInterpolant;

  GLTFCubicSplineInterpolant.prototype.copySampleValue_ = function ( index ) {

    // Copies a sample value to the result buffer. See description of glTF
    // CUBICSPLINE values layout in interpolate_() function below.

    var result = this.resultBuffer,
      values = this.sampleValues,
      valueSize = this.valueSize,
      offset = index * valueSize * 3 + valueSize;

    for ( var i = 0; i !== valueSize; i ++ ) {

      result[ i ] = values[ offset + i ];

    }

    return result;

  };

  GLTFCubicSplineInterpolant.prototype.beforeStart_ = GLTFCubicSplineInterpolant.prototype.copySampleValue_;

  GLTFCubicSplineInterpolant.prototype.afterEnd_ = GLTFCubicSplineInterpolant.prototype.copySampleValue_;

  GLTFCubicSplineInterpolant.prototype.interpolate_ = function ( i1, t0, t, t1 ) {

    var result = this.resultBuffer;
    var values = this.sampleValues;
    var stride = this.valueSize;

    var stride2 = stride * 2;
    var stride3 = stride * 3;

    var td = t1 - t0;

    var p = ( t - t0 ) / td;
    var pp = p * p;
    var ppp = pp * p;

    var offset1 = i1 * stride3;
    var offset0 = offset1 - stride3;

    var s2 = - 2 * ppp + 3 * pp;
    var s3 = ppp - pp;
    var s0 = 1 - s2;
    var s1 = s3 - pp + p;

    // Layout of keyframe output values for CUBICSPLINE animations:
    //   [ inTangent_1, splineVertex_1, outTangent_1, inTangent_2, splineVertex_2, ... ]
    for ( var i = 0; i !== stride; i ++ ) {

      var p0 = values[ offset0 + i + stride ]; // splineVertex_k
      var m0 = values[ offset0 + i + stride2 ] * td; // outTangent_k * (t_k+1 - t_k)
      var p1 = values[ offset1 + i + stride ]; // splineVertex_k+1
      var m1 = values[ offset1 + i ] * td; // inTangent_k+1 * (t_k+1 - t_k)

      result[ i ] = s0 * p0 + s1 * m0 + s2 * p1 + s3 * m1;

    }

    return result;

  };

  /*********************************/
  /********** INTERNALS ************/
  /*********************************/

  /* CONSTANTS */

  var WEBGL_CONSTANTS = {
    FLOAT: 5126,
    //FLOAT_MAT2: 35674,
    FLOAT_MAT3: 35675,
    FLOAT_MAT4: 35676,
    FLOAT_VEC2: 35664,
    FLOAT_VEC3: 35665,
    FLOAT_VEC4: 35666,
    LINEAR: 9729,
    REPEAT: 10497,
    SAMPLER_2D: 35678,
    POINTS: 0,
    LINES: 1,
    LINE_LOOP: 2,
    LINE_STRIP: 3,
    TRIANGLES: 4,
    TRIANGLE_STRIP: 5,
    TRIANGLE_FAN: 6,
    UNSIGNED_BYTE: 5121,
    UNSIGNED_SHORT: 5123
  };

  var WEBGL_COMPONENT_TYPES = {
    5120: Int8Array,
    5121: Uint8Array,
    5122: Int16Array,
    5123: Uint16Array,
    5125: Uint32Array,
    5126: Float32Array
  };

  var WEBGL_FILTERS = {
    9728: NearestFilter,
    9729: LinearFilter,
    9984: NearestMipmapNearestFilter,
    9985: LinearMipmapNearestFilter,
    9986: NearestMipmapLinearFilter,
    9987: LinearMipmapLinearFilter
  };

  var WEBGL_WRAPPINGS = {
    33071: ClampToEdgeWrapping,
    33648: MirroredRepeatWrapping,
    10497: RepeatWrapping
  };

  var WEBGL_TYPE_SIZES = {
    'SCALAR': 1,
    'VEC2': 2,
    'VEC3': 3,
    'VEC4': 4,
    'MAT2': 4,
    'MAT3': 9,
    'MAT4': 16
  };

  var ATTRIBUTES = {
    POSITION: 'position',
    NORMAL: 'normal',
    TANGENT: 'tangent',
    TEXCOORD_0: 'uv',
    TEXCOORD_1: 'uv2',
    COLOR_0: 'color',
    WEIGHTS_0: 'skinWeight',
    JOINTS_0: 'skinIndex',
  };

  var PATH_PROPERTIES = {
    scale: 'scale',
    translation: 'position',
    rotation: 'quaternion',
    weights: 'morphTargetInfluences'
  };

  var INTERPOLATION = {
    CUBICSPLINE: undefined, // We use a custom interpolant (GLTFCubicSplineInterpolation) for CUBICSPLINE tracks. Each
                            // keyframe track will be initialized with a default interpolation type, then modified.
    LINEAR: InterpolateLinear,
    STEP: InterpolateDiscrete
  };

  var ALPHA_MODES = {
    OPAQUE: 'OPAQUE',
    MASK: 'MASK',
    BLEND: 'BLEND'
  };

  /* UTILITY FUNCTIONS */

  function resolveURL( url, path ) {

    // Invalid URL
    if ( typeof url !== 'string' || url === '' ) return '';

    // Host Relative URL
    if ( /^https?:\/\//i.test( path ) && /^\//.test( url ) ) {

      path = path.replace( /(^https?:\/\/[^\/]+).*/i, '$1' );

    }

    // Absolute URL http://,https://,//
    if ( /^(https?:)?\/\//i.test( url ) ) return url;

    // Data URI
    if ( /^data:.*,.*$/i.test( url ) ) return url;

    // Blob URL
    if ( /^blob:.*$/i.test( url ) ) return url;

    // Relative URL
    return path + url;

  }

  /**
   * Specification: https://github.com/KhronosGroup/glTF/blob/master/specification/2.0/README.md#default-material
   */
  function createDefaultMaterial( cache ) {

    if ( cache[ 'DefaultMaterial' ] === undefined ) {

      cache[ 'DefaultMaterial' ] = new MeshStandardMaterial( {
        color: 0xFFFFFF,
        emissive: 0x000000,
        metalness: 1,
        roughness: 1,
        transparent: false,
        depthTest: true,
        side: FrontSide
      } );

    }

    return cache[ 'DefaultMaterial' ];

  }

  function addUnknownExtensionsToUserData( knownExtensions, object, objectDef ) {

    // Add unknown glTF extensions to an object's userData.

    for ( var name in objectDef.extensions ) {

      if ( knownExtensions[ name ] === undefined ) {

        object.userData.gltfExtensions = object.userData.gltfExtensions || {};
        object.userData.gltfExtensions[ name ] = objectDef.extensions[ name ];

      }

    }

  }

  /**
   * @param {Object3D|Material|BufferGeometry} object
   * @param {GLTF.definition} gltfDef
   */
  function assignExtrasToUserData( object, gltfDef ) {

    if ( gltfDef.extras !== undefined ) {

      if ( typeof gltfDef.extras === 'object' ) {

        Object.assign( object.userData, gltfDef.extras );

      } else {

        console.warn( 'THREE.GLTFLoader: Ignoring primitive type .extras, ' + gltfDef.extras );

      }

    }

  }

  /**
   * Specification: https://github.com/KhronosGroup/glTF/blob/master/specification/2.0/README.md#morph-targets
   *
   * @param {BufferGeometry} geometry
   * @param {Array<GLTF.Target>} targets
   * @param {GLTFParser} parser
   * @return {Promise<BufferGeometry>}
   */
  function addMorphTargets( geometry, targets, parser ) {

    var hasMorphPosition = false;
    var hasMorphNormal = false;

    for ( var i = 0, il = targets.length; i < il; i ++ ) {

      var target = targets[ i ];

      if ( target.POSITION !== undefined ) hasMorphPosition = true;
      if ( target.NORMAL !== undefined ) hasMorphNormal = true;

      if ( hasMorphPosition && hasMorphNormal ) break;

    }

    if ( ! hasMorphPosition && ! hasMorphNormal ) return Promise.resolve( geometry );

    var pendingPositionAccessors = [];
    var pendingNormalAccessors = [];

    for ( var i = 0, il = targets.length; i < il; i ++ ) {

      var target = targets[ i ];

      if ( hasMorphPosition ) {

        var pendingAccessor = target.POSITION !== undefined
          ? parser.getDependency( 'accessor', target.POSITION )
          : geometry.attributes.position;

        pendingPositionAccessors.push( pendingAccessor );

      }

      if ( hasMorphNormal ) {

        var pendingAccessor = target.NORMAL !== undefined
          ? parser.getDependency( 'accessor', target.NORMAL )
          : geometry.attributes.normal;

        pendingNormalAccessors.push( pendingAccessor );

      }

    }

    return Promise.all( [
      Promise.all( pendingPositionAccessors ),
      Promise.all( pendingNormalAccessors )
    ] ).then( function ( accessors ) {

      var morphPositions = accessors[ 0 ];
      var morphNormals = accessors[ 1 ];

      if ( hasMorphPosition ) geometry.morphAttributes.position = morphPositions;
      if ( hasMorphNormal ) geometry.morphAttributes.normal = morphNormals;
      geometry.morphTargetsRelative = true;

      return geometry;

    } );

  }

  /**
   * @param {Mesh} mesh
   * @param {GLTF.Mesh} meshDef
   */
  function updateMorphTargets( mesh, meshDef ) {

    mesh.updateMorphTargets();

    if ( meshDef.weights !== undefined ) {

      for ( var i = 0, il = meshDef.weights.length; i < il; i ++ ) {

        mesh.morphTargetInfluences[ i ] = meshDef.weights[ i ];

      }

    }

    // .extras has user-defined data, so check that .extras.targetNames is an array.
    if ( meshDef.extras && Array.isArray( meshDef.extras.targetNames ) ) {

      var targetNames = meshDef.extras.targetNames;

      if ( mesh.morphTargetInfluences.length === targetNames.length ) {

        mesh.morphTargetDictionary = {};

        for ( var i = 0, il = targetNames.length; i < il; i ++ ) {

          mesh.morphTargetDictionary[ targetNames[ i ] ] = i;

        }

      } else {

        console.warn( 'THREE.GLTFLoader: Invalid extras.targetNames length. Ignoring names.' );

      }

    }

  }

  function createPrimitiveKey( primitiveDef ) {

    var dracoExtension = primitiveDef.extensions && primitiveDef.extensions[ EXTENSIONS.KHR_DRACO_MESH_COMPRESSION ];
    var geometryKey;

    if ( dracoExtension ) {

      geometryKey = 'draco:' + dracoExtension.bufferView
        + ':' + dracoExtension.indices
        + ':' + createAttributesKey( dracoExtension.attributes );

    } else {

      geometryKey = primitiveDef.indices + ':' + createAttributesKey( primitiveDef.attributes ) + ':' + primitiveDef.mode;

    }

    return geometryKey;

  }

  function createAttributesKey( attributes ) {

    var attributesKey = '';

    var keys = Object.keys( attributes ).sort();

    for ( var i = 0, il = keys.length; i < il; i ++ ) {

      attributesKey += keys[ i ] + ':' + attributes[ keys[ i ] ] + ';';

    }

    return attributesKey;

  }

  /* GLTF PARSER */

  function GLTFParser( json, options ) {

    this.json = json || {};
    this.extensions = {};
    this.plugins = {};
    this.options = options || {};

    // loader object cache
    this.cache = new GLTFRegistry();

    // associations between Three.js objects and glTF elements
    this.associations = new Map();

    // BufferGeometry caching
    this.primitiveCache = {};

    // Object3D instance caches
    this.meshCache = { refs: {}, uses: {} };
    this.cameraCache = { refs: {}, uses: {} };
    this.lightCache = { refs: {}, uses: {} };

    // Use an ImageBitmapLoader if imageBitmaps are supported. Moves much of the
    // expensive work of uploading a texture to the GPU off the main thread.
    if ( typeof createImageBitmap !== 'undefined' && /Firefox/.test( navigator.userAgent ) === false ) {

      this.textureLoader = new ImageBitmapLoader( this.options.manager );

    } else {

      this.textureLoader = new TextureLoader( this.options.manager );

    }

    this.textureLoader.setCrossOrigin( this.options.crossOrigin );

    this.fileLoader = new FileLoader( this.options.manager );
    this.fileLoader.setResponseType( 'arraybuffer' );

    if ( this.options.crossOrigin === 'use-credentials' ) {

      this.fileLoader.setWithCredentials( true );

    }

  }

  GLTFParser.prototype.setExtensions = function ( extensions ) {

    this.extensions = extensions;

  };

  GLTFParser.prototype.setPlugins = function ( plugins ) {

    this.plugins = plugins;

  };

  GLTFParser.prototype.parse = function ( onLoad, onError ) {

    var parser = this;
    var json = this.json;
    var extensions = this.extensions;

    // Clear the loader cache
    this.cache.removeAll();

    // Mark the special nodes/meshes in json for efficient parse
    this._markDefs();

    Promise.all( [

      this.getDependencies( 'scene' ),
      this.getDependencies( 'animation' ),
      this.getDependencies( 'camera' ),

    ] ).then( function ( dependencies ) {

      var result = {
        scene: dependencies[ 0 ][ json.scene || 0 ],
        scenes: dependencies[ 0 ],
        animations: dependencies[ 1 ],
        cameras: dependencies[ 2 ],
        asset: json.asset,
        parser: parser,
        userData: {}
      };

      addUnknownExtensionsToUserData( extensions, result, json );

      assignExtrasToUserData( result, json );

      onLoad( result );

    } ).catch( onError );

  };

  /**
   * Marks the special nodes/meshes in json for efficient parse.
   */
  GLTFParser.prototype._markDefs = function () {

    var nodeDefs = this.json.nodes || [];
    var skinDefs = this.json.skins || [];
    var meshDefs = this.json.meshes || [];

    // Nothing in the node definition indicates whether it is a Bone or an
    // Object3D. Use the skins' joint references to mark bones.
    for ( var skinIndex = 0, skinLength = skinDefs.length; skinIndex < skinLength; skinIndex ++ ) {

      var joints = skinDefs[ skinIndex ].joints;

      for ( var i = 0, il = joints.length; i < il; i ++ ) {

        nodeDefs[ joints[ i ] ].isBone = true;

      }

    }

    // Iterate over all nodes, marking references to shared resources,
    // as well as skeleton joints.
    for ( var nodeIndex = 0, nodeLength = nodeDefs.length; nodeIndex < nodeLength; nodeIndex ++ ) {

      var nodeDef = nodeDefs[ nodeIndex ];

      if ( nodeDef.mesh !== undefined ) {

        this._addNodeRef( this.meshCache, nodeDef.mesh );

        // Nothing in the mesh definition indicates whether it is
        // a SkinnedMesh or Mesh. Use the node's mesh reference
        // to mark SkinnedMesh if node has skin.
        if ( nodeDef.skin !== undefined ) {

          meshDefs[ nodeDef.mesh ].isSkinnedMesh = true;

        }

      }

      if ( nodeDef.camera !== undefined ) {

        this._addNodeRef( this.cameraCache, nodeDef.camera );

      }

      if ( nodeDef.extensions
        && nodeDef.extensions[ EXTENSIONS.KHR_LIGHTS_PUNCTUAL ]
        && nodeDef.extensions[ EXTENSIONS.KHR_LIGHTS_PUNCTUAL ].light !== undefined ) {

        this._addNodeRef( this.lightCache, nodeDef.extensions[ EXTENSIONS.KHR_LIGHTS_PUNCTUAL ].light );

      }

    }

  };

  /**
   * Counts references to shared node / Object3D resources. These resources
   * can be reused, or 'instantiated', at multiple nodes in the scene
   * hierarchy. Mesh, Camera, and Light instances are instantiated and must
   * be marked. Non-scenegraph resources (like Materials, Geometries, and
   * Textures) can be reused directly and are not marked here.
   *
   * Example: CesiumMilkTruck sample model reuses 'Wheel' meshes.
   */
  GLTFParser.prototype._addNodeRef = function ( cache, index ) {

    if ( index === undefined ) return;

    if ( cache.refs[ index ] === undefined ) {

      cache.refs[ index ] = cache.uses[ index ] = 0;

    }

    cache.refs[ index ] ++;

  };

  /** Returns a reference to a shared resource, cloning it if necessary. */
  GLTFParser.prototype._getNodeRef = function ( cache, index, object ) {

    if ( cache.refs[ index ] <= 1 ) return object;

    var ref = object.clone();

    ref.name += '_instance_' + ( cache.uses[ index ] ++ );

    return ref;

  };

  GLTFParser.prototype._invokeOne = function ( func ) {

    var extensions = Object.values( this.plugins );
    extensions.push( this );

    for ( var i = 0; i < extensions.length; i ++ ) {

      var result = func( extensions[ i ] );

      if ( result ) return result;

    }

  };

  GLTFParser.prototype._invokeAll = function ( func ) {

    var extensions = Object.values( this.plugins );
    extensions.unshift( this );

    var pending = [];

    for ( var i = 0; i < extensions.length; i ++ ) {

      pending.push( func( extensions[ i ] ) );

    }

    return Promise.all( pending );

  };

  /**
   * Requests the specified dependency asynchronously, with caching.
   * @param {string} type
   * @param {number} index
   * @return {Promise<Object3D|Material|THREE.Texture|AnimationClip|ArrayBuffer|Object>}
   */
  GLTFParser.prototype.getDependency = function ( type, index ) {

    var cacheKey = type + ':' + index;
    var dependency = this.cache.get( cacheKey );

    if ( ! dependency ) {

      switch ( type ) {

        case 'scene':
          dependency = this.loadScene( index );
          break;

        case 'node':
          dependency = this.loadNode( index );
          break;

        case 'mesh':
          dependency = this._invokeOne( function ( ext ) {

            return ext.loadMesh && ext.loadMesh( index );

          } );
          break;

        case 'accessor':
          dependency = this.loadAccessor( index );
          break;

        case 'bufferView':
          dependency = this._invokeOne( function ( ext ) {

            return ext.loadBufferView && ext.loadBufferView( index );

          } );
          break;

        case 'buffer':
          dependency = this.loadBuffer( index );
          break;

        case 'material':
          dependency = this._invokeOne( function ( ext ) {

            return ext.loadMaterial && ext.loadMaterial( index );

          } );
          break;

        case 'texture':
          break;

        case 'skin':
          dependency = this.loadSkin( index );
          break;

        case 'animation':
          dependency = this.loadAnimation( index );
          break;

        case 'camera':
          dependency = this.loadCamera( index );
          break;

        case 'light':
          dependency = this.extensions[ EXTENSIONS.KHR_LIGHTS_PUNCTUAL ].loadLight( index );
          break;

        default:
          throw new Error( 'Unknown type: ' + type );

      }

      this.cache.add( cacheKey, dependency );

    }

    return dependency;

  };

  /**
   * Requests all dependencies of the specified type asynchronously, with caching.
   * @param {string} type
   * @return {Promise<Array<Object>>}
   */
  GLTFParser.prototype.getDependencies = function ( type ) {

    var dependencies = this.cache.get( type );

    if ( ! dependencies ) {

      var parser = this;
      var defs = this.json[ type + ( type === 'mesh' ? 'es' : 's' ) ] || [];

      dependencies = Promise.all( defs.map( function ( def, index ) {

        return parser.getDependency( type, index );

      } ) );

      this.cache.add( type, dependencies );

    }

    return dependencies;

  };

  /**
   * Specification: https://github.com/KhronosGroup/glTF/blob/master/specification/2.0/README.md#buffers-and-buffer-views
   * @param {number} bufferIndex
   * @return {Promise<ArrayBuffer>}
   */
  GLTFParser.prototype.loadBuffer = function ( bufferIndex ) {

    var bufferDef = this.json.buffers[ bufferIndex ];
    var loader = this.fileLoader;

    if ( bufferDef.type && bufferDef.type !== 'arraybuffer' ) {

      throw new Error( 'THREE.GLTFLoader: ' + bufferDef.type + ' buffer type is not supported.' );

    }

    // If present, GLB container is required to be the first buffer.
    if ( bufferDef.uri === undefined && bufferIndex === 0 ) {

      return Promise.resolve( this.extensions[ EXTENSIONS.KHR_BINARY_GLTF ].body );

    }

    var options = this.options;

    return new Promise( function ( resolve, reject ) {

      loader.load( resolveURL( bufferDef.uri, options.path ), resolve, undefined, function () {

        reject( new Error( 'THREE.GLTFLoader: Failed to load buffer ' + bufferDef.uri + '.' ) );

      } );

    } );

  };

  /**
   * Specification: https://github.com/KhronosGroup/glTF/blob/master/specification/2.0/README.md#buffers-and-buffer-views
   * @param {number} bufferViewIndex
   * @return {Promise<ArrayBuffer>}
   */
  GLTFParser.prototype.loadBufferView = function ( bufferViewIndex ) {

    var bufferViewDef = this.json.bufferViews[ bufferViewIndex ];

    return this.getDependency( 'buffer', bufferViewDef.buffer ).then( function ( buffer ) {

      var byteLength = bufferViewDef.byteLength || 0;
      var byteOffset = bufferViewDef.byteOffset || 0;
      return buffer.slice( byteOffset, byteOffset + byteLength );

    } );

  };

  /**
   * Specification: https://github.com/KhronosGroup/glTF/blob/master/specification/2.0/README.md#accessors
   * @param {number} accessorIndex
   * @return {Promise<BufferAttribute|InterleavedBufferAttribute>}
   */
  GLTFParser.prototype.loadAccessor = function ( accessorIndex ) {

    var parser = this;
    var json = this.json;

    var accessorDef = this.json.accessors[ accessorIndex ];

    if ( accessorDef.bufferView === undefined && accessorDef.sparse === undefined ) {

      // Ignore empty accessors, which may be used to declare runtime
      // information about attributes coming from another source (e.g. Draco
      // compression extension).
      return Promise.resolve( null );

    }

    var pendingBufferViews = [];

    if ( accessorDef.bufferView !== undefined ) {

      pendingBufferViews.push( this.getDependency( 'bufferView', accessorDef.bufferView ) );

    } else {

      pendingBufferViews.push( null );

    }

    if ( accessorDef.sparse !== undefined ) {

      pendingBufferViews.push( this.getDependency( 'bufferView', accessorDef.sparse.indices.bufferView ) );
      pendingBufferViews.push( this.getDependency( 'bufferView', accessorDef.sparse.values.bufferView ) );

    }

    return Promise.all( pendingBufferViews ).then( function ( bufferViews ) {

      var bufferView = bufferViews[ 0 ];

      var itemSize = WEBGL_TYPE_SIZES[ accessorDef.type ];
      var TypedArray = WEBGL_COMPONENT_TYPES[ accessorDef.componentType ];

      // For VEC3: itemSize is 3, elementBytes is 4, itemBytes is 12.
      var elementBytes = TypedArray.BYTES_PER_ELEMENT;
      var itemBytes = elementBytes * itemSize;
      var byteOffset = accessorDef.byteOffset || 0;
      var byteStride = accessorDef.bufferView !== undefined ? json.bufferViews[ accessorDef.bufferView ].byteStride : undefined;
      var normalized = accessorDef.normalized === true;
      var array, bufferAttribute;

      // The buffer is not interleaved if the stride is the item size in bytes.
      if ( byteStride && byteStride !== itemBytes ) {

        // Each 'slice' of the buffer, as defined by 'count' elements of 'byteStride' bytes, gets its own InterleavedBuffer
        // This makes sure that IBA.count reflects accessor.count properly
        var ibSlice = Math.floor( byteOffset / byteStride );
        var ibCacheKey = 'InterleavedBuffer:' + accessorDef.bufferView + ':' + accessorDef.componentType + ':' + ibSlice + ':' + accessorDef.count;
        var ib = parser.cache.get( ibCacheKey );

        if ( ! ib ) {

          array = new TypedArray( bufferView, ibSlice * byteStride, accessorDef.count * byteStride / elementBytes );

          // Integer parameters to IB/IBA are in array elements, not bytes.
          ib = new InterleavedBuffer( array, byteStride / elementBytes );

          parser.cache.add( ibCacheKey, ib );

        }

        bufferAttribute = new InterleavedBufferAttribute( ib, itemSize, ( byteOffset % byteStride ) / elementBytes, normalized );

      } else {

        if ( bufferView === null ) {

          array = new TypedArray( accessorDef.count * itemSize );

        } else {

          array = new TypedArray( bufferView, byteOffset, accessorDef.count * itemSize );

        }

        bufferAttribute = new BufferAttribute( array, itemSize, normalized );

      }

      // https://github.com/KhronosGroup/glTF/blob/master/specification/2.0/README.md#sparse-accessors
      if ( accessorDef.sparse !== undefined ) {

        var itemSizeIndices = WEBGL_TYPE_SIZES.SCALAR;
        var TypedArrayIndices = WEBGL_COMPONENT_TYPES[ accessorDef.sparse.indices.componentType ];

        var byteOffsetIndices = accessorDef.sparse.indices.byteOffset || 0;
        var byteOffsetValues = accessorDef.sparse.values.byteOffset || 0;

        var sparseIndices = new TypedArrayIndices( bufferViews[ 1 ], byteOffsetIndices, accessorDef.sparse.count * itemSizeIndices );
        var sparseValues = new TypedArray( bufferViews[ 2 ], byteOffsetValues, accessorDef.sparse.count * itemSize );

        if ( bufferView !== null ) {

          // Avoid modifying the original ArrayBuffer, if the bufferView wasn't initialized with zeroes.
          bufferAttribute = new BufferAttribute( bufferAttribute.array.slice(), bufferAttribute.itemSize, bufferAttribute.normalized );

        }

        for ( var i = 0, il = sparseIndices.length; i < il; i ++ ) {

          var index = sparseIndices[ i ];

          bufferAttribute.setX( index, sparseValues[ i * itemSize ] );
          if ( itemSize >= 2 ) bufferAttribute.setY( index, sparseValues[ i * itemSize + 1 ] );
          if ( itemSize >= 3 ) bufferAttribute.setZ( index, sparseValues[ i * itemSize + 2 ] );
          if ( itemSize >= 4 ) bufferAttribute.setW( index, sparseValues[ i * itemSize + 3 ] );
          if ( itemSize >= 5 ) throw new Error( 'THREE.GLTFLoader: Unsupported itemSize in sparse BufferAttribute.' );

        }

      }

      return bufferAttribute;

    } );

  };

  /**
   * Assigns final material to a Mesh, Line, or Points instance. The instance
   * already has a material (generated from the glTF material options alone)
   * but reuse of the same glTF material may require multiple threejs materials
   * to accomodate different primitive types, defines, etc. New materials will
   * be created if necessary, and reused from a cache.
   * @param  {Object3D} mesh Mesh, Line, or Points instance.
   */
  GLTFParser.prototype.assignFinalMaterial = function ( mesh ) {

    var geometry = mesh.geometry;
    var material = mesh.material;

    var useVertexTangents = geometry.attributes.tangent !== undefined;
    var useVertexColors = geometry.attributes.color !== undefined;
    var useFlatShading = geometry.attributes.normal === undefined;
    var useSkinning = mesh.isSkinnedMesh === true;
    var useMorphTargets = Object.keys( geometry.morphAttributes ).length > 0;
    var useMorphNormals = useMorphTargets && geometry.morphAttributes.normal !== undefined;

    if ( mesh.isPoints ) {

      var cacheKey = 'PointsMaterial:' + material.uuid;

      var pointsMaterial = this.cache.get( cacheKey );

      if ( ! pointsMaterial ) {

        pointsMaterial = new PointsMaterial();
        Material.prototype.copy.call( pointsMaterial, material );
        pointsMaterial.color.copy( material.color );
        pointsMaterial.map = material.map;
        pointsMaterial.sizeAttenuation = false; // glTF spec says points should be 1px

        this.cache.add( cacheKey, pointsMaterial );

      }

      material = pointsMaterial;

    } else if ( mesh.isLine ) {

      var cacheKey = 'LineBasicMaterial:' + material.uuid;

      var lineMaterial = this.cache.get( cacheKey );

      if ( ! lineMaterial ) {

        lineMaterial = new LineBasicMaterial();
        Material.prototype.copy.call( lineMaterial, material );
        lineMaterial.color.copy( material.color );

        this.cache.add( cacheKey, lineMaterial );

      }

      material = lineMaterial;

    }

    // Clone the material if it will be modified
    if ( useVertexTangents || useVertexColors || useFlatShading || useSkinning || useMorphTargets ) {

      var cacheKey = 'ClonedMaterial:' + material.uuid + ':';

      if ( material.isGLTFSpecularGlossinessMaterial ) cacheKey += 'specular-glossiness:';
      if ( useSkinning ) cacheKey += 'skinning:';
      if ( useVertexTangents ) cacheKey += 'vertex-tangents:';
      if ( useVertexColors ) cacheKey += 'vertex-colors:';
      if ( useFlatShading ) cacheKey += 'flat-shading:';
      if ( useMorphTargets ) cacheKey += 'morph-targets:';
      if ( useMorphNormals ) cacheKey += 'morph-normals:';

      var cachedMaterial = this.cache.get( cacheKey );

      if ( ! cachedMaterial ) {

        cachedMaterial = material.clone();

        if ( useSkinning ) cachedMaterial.skinning = true;
        if ( useVertexTangents ) cachedMaterial.vertexTangents = true;
        if ( useVertexColors ) cachedMaterial.vertexColors = true;
        if ( useFlatShading ) cachedMaterial.flatShading = true;
        if ( useMorphTargets ) cachedMaterial.morphTargets = true;
        if ( useMorphNormals ) cachedMaterial.morphNormals = true;

        this.cache.add( cacheKey, cachedMaterial );

        this.associations.set( cachedMaterial, this.associations.get( material ) );

      }

      material = cachedMaterial;

    }

    // workarounds for mesh and geometry

    if ( material.aoMap && geometry.attributes.uv2 === undefined && geometry.attributes.uv !== undefined ) {

      geometry.setAttribute( 'uv2', geometry.attributes.uv );

    }

    // https://github.com/mrdoob/three.js/issues/11438#issuecomment-507003995
    if ( material.normalScale && ! useVertexTangents ) {

      material.normalScale.y = - material.normalScale.y;

    }

    if ( material.clearcoatNormalScale && ! useVertexTangents ) {

      material.clearcoatNormalScale.y = - material.clearcoatNormalScale.y;

    }

    mesh.material = material;

  };

  GLTFParser.prototype.getMaterialType = function ( /* materialIndex */ ) {

    return MeshStandardMaterial;

  };

  /**
   * Specification: https://github.com/KhronosGroup/glTF/blob/master/specification/2.0/README.md#materials
   * @param {number} materialIndex
   * @return {Promise<Material>}
   */
  GLTFParser.prototype.loadMaterial = function ( materialIndex ) {

    var parser = this;
    var json = this.json;
    var extensions = this.extensions;
    var materialDef = json.materials[ materialIndex ];

    var materialType;
    var materialParams = {};
    var materialExtensions = materialDef.extensions || {};

    var pending = [];

    if ( materialExtensions[ EXTENSIONS.KHR_MATERIALS_PBR_SPECULAR_GLOSSINESS ] ) {

      var sgExtension = extensions[ EXTENSIONS.KHR_MATERIALS_PBR_SPECULAR_GLOSSINESS ];
      materialType = sgExtension.getMaterialType();
      pending.push( sgExtension.extendParams( materialParams, materialDef, parser ) );

    } else if ( materialExtensions[ EXTENSIONS.KHR_MATERIALS_UNLIT ] ) {

      var kmuExtension = extensions[ EXTENSIONS.KHR_MATERIALS_UNLIT ];
      materialType = kmuExtension.getMaterialType();
      pending.push( kmuExtension.extendParams( materialParams, materialDef, parser ) );

    } else {

      // Specification:
      // https://github.com/KhronosGroup/glTF/tree/master/specification/2.0#metallic-roughness-material

      var metallicRoughness = materialDef.pbrMetallicRoughness || {};

      materialParams.color = new Color( 1.0, 1.0, 1.0 );
      materialParams.opacity = 1.0;

      if ( Array.isArray( metallicRoughness.baseColorFactor ) ) {

        var array = metallicRoughness.baseColorFactor;

        materialParams.color.fromArray( array );
        materialParams.opacity = array[ 3 ];

      }

      materialType = this._invokeOne( function ( ext ) {

        return ext.getMaterialType && ext.getMaterialType( materialIndex );

      } );

      pending.push( this._invokeAll( function ( ext ) {

        return ext.extendMaterialParams && ext.extendMaterialParams( materialIndex, materialParams );

      } ) );

    }

    if ( materialDef.doubleSided === true ) {

      materialParams.side = DoubleSide;

    }

    var alphaMode = materialDef.alphaMode || ALPHA_MODES.OPAQUE;

    if ( alphaMode === ALPHA_MODES.BLEND ) {

      materialParams.transparent = true;

      // See: https://github.com/mrdoob/three.js/issues/17706
      materialParams.depthWrite = false;

    } else {

      materialParams.transparent = false;

      if ( alphaMode === ALPHA_MODES.MASK ) {

        materialParams.alphaTest = materialDef.alphaCutoff !== undefined ? materialDef.alphaCutoff : 0.5;

      }

    }

    if ( materialDef.emissiveFactor !== undefined && materialType !== MeshBasicMaterial ) {

      materialParams.emissive = new Color().fromArray( materialDef.emissiveFactor );

    }

    return Promise.all( pending ).then( function () {

      var material;

      if ( materialType === GLTFMeshStandardSGMaterial ) {

        material = extensions[ EXTENSIONS.KHR_MATERIALS_PBR_SPECULAR_GLOSSINESS ].createMaterial( materialParams );

      } else {

        material = new materialType( materialParams );

      }

      if ( materialDef.name ) material.name = materialDef.name;

      // baseColorTexture, emissiveTexture, and specularGlossinessTexture use sRGB encoding.
      if ( material.map ) material.map.encoding = sRGBEncoding;
      if ( material.emissiveMap ) material.emissiveMap.encoding = sRGBEncoding;

      assignExtrasToUserData( material, materialDef );

      parser.associations.set( material, { type: 'materials', index: materialIndex } );

      if ( materialDef.extensions ) addUnknownExtensionsToUserData( extensions, material, materialDef );

      return material;

    } );

  };

  /**
   * @param {BufferGeometry} geometry
   * @param {GLTF.Primitive} primitiveDef
   * @param {GLTFParser} parser
   */
  function computeBounds( geometry, primitiveDef, parser ) {

    var attributes = primitiveDef.attributes;

    var box = new Box3();

    if ( attributes.POSITION !== undefined ) {

      var accessor = parser.json.accessors[ attributes.POSITION ];

      var min = accessor.min;
      var max = accessor.max;

      // glTF requires 'min' and 'max', but VRM (which extends glTF) currently ignores that requirement.

      if ( min !== undefined && max !== undefined ) {

        box.set(
          new Vector3( min[ 0 ], min[ 1 ], min[ 2 ] ),
          new Vector3( max[ 0 ], max[ 1 ], max[ 2 ] ) );

      } else {

        console.warn( 'THREE.GLTFLoader: Missing min/max properties for accessor POSITION.' );

        return;

      }

    } else {

      return;

    }

    var targets = primitiveDef.targets;

    if ( targets !== undefined ) {

      var maxDisplacement = new Vector3();
      var vector = new Vector3();

      for ( var i = 0, il = targets.length; i < il; i ++ ) {

        var target = targets[ i ];

        if ( target.POSITION !== undefined ) {

          var accessor = parser.json.accessors[ target.POSITION ];
          var min = accessor.min;
          var max = accessor.max;

          // glTF requires 'min' and 'max', but VRM (which extends glTF) currently ignores that requirement.

          if ( min !== undefined && max !== undefined ) {

            // we need to get max of absolute components because target weight is [-1,1]
            vector.setX( Math.max( Math.abs( min[ 0 ] ), Math.abs( max[ 0 ] ) ) );
            vector.setY( Math.max( Math.abs( min[ 1 ] ), Math.abs( max[ 1 ] ) ) );
            vector.setZ( Math.max( Math.abs( min[ 2 ] ), Math.abs( max[ 2 ] ) ) );

            // Note: this assumes that the sum of all weights is at most 1. This isn't quite correct - it's more conservative
            // to assume that each target can have a max weight of 1. However, for some use cases - notably, when morph targets
            // are used to implement key-frame animations and as such only two are active at a time - this results in very large
            // boxes. So for now we make a box that's sometimes a touch too small but is hopefully mostly of reasonable size.
            maxDisplacement.max( vector );

          } else {

            console.warn( 'THREE.GLTFLoader: Missing min/max properties for accessor POSITION.' );

          }

        }

      }

      // As per comment above this box isn't conservative, but has a reasonable size for a very large number of morph targets.
      box.expandByVector( maxDisplacement );

    }

    geometry.boundingBox = box;

    var sphere = new Sphere();

    box.getCenter( sphere.center );
    sphere.radius = box.min.distanceTo( box.max ) / 2;

    geometry.boundingSphere = sphere;

  }

  /**
   * @param {BufferGeometry} geometry
   * @param {GLTF.Primitive} primitiveDef
   * @param {GLTFParser} parser
   * @return {Promise<BufferGeometry>}
   */
  function addPrimitiveAttributes( geometry, primitiveDef, parser ) {

    var attributes = primitiveDef.attributes;

    var pending = [];

    function assignAttributeAccessor( accessorIndex, attributeName ) {

      return parser.getDependency( 'accessor', accessorIndex )
        .then( function ( accessor ) {

          geometry.setAttribute( attributeName, accessor );

        } );

    }

    for ( var gltfAttributeName in attributes ) {

      var threeAttributeName = ATTRIBUTES[ gltfAttributeName ] || gltfAttributeName.toLowerCase();

      // Skip attributes already provided by e.g. Draco extension.
      if ( threeAttributeName in geometry.attributes ) continue;

      pending.push( assignAttributeAccessor( attributes[ gltfAttributeName ], threeAttributeName ) );

    }

    if ( primitiveDef.indices !== undefined && ! geometry.index ) {

      var accessor = parser.getDependency( 'accessor', primitiveDef.indices ).then( function ( accessor ) {

        geometry.setIndex( accessor );

      } );

      pending.push( accessor );

    }

    assignExtrasToUserData( geometry, primitiveDef );

    computeBounds( geometry, primitiveDef, parser );

    return Promise.all( pending ).then( function () {

      return primitiveDef.targets !== undefined
        ? addMorphTargets( geometry, primitiveDef.targets, parser )
        : geometry;

    } );

  }

  /**
   * @param {BufferGeometry} geometry
   * @param {Number} drawMode
   * @return {BufferGeometry}
   */
  function toTrianglesDrawMode( geometry, drawMode ) {

    var index = geometry.getIndex();

    // generate index if not present

    if ( index === null ) {

      var indices = [];

      var position = geometry.getAttribute( 'position' );

      if ( position !== undefined ) {

        for ( var i = 0; i < position.count; i ++ ) {

          indices.push( i );

        }

        geometry.setIndex( indices );
        index = geometry.getIndex();

      } else {

        console.error( 'THREE.GLTFLoader.toTrianglesDrawMode(): Undefined position attribute. Processing not possible.' );
        return geometry;

      }

    }

    //

    var numberOfTriangles = index.count - 2;
    var newIndices = [];

    if ( drawMode === TriangleFanDrawMode ) {

      // gl.TRIANGLE_FAN

      for ( var i = 1; i <= numberOfTriangles; i ++ ) {

        newIndices.push( index.getX( 0 ) );
        newIndices.push( index.getX( i ) );
        newIndices.push( index.getX( i + 1 ) );

      }

    } else {

      // gl.TRIANGLE_STRIP

      for ( var i = 0; i < numberOfTriangles; i ++ ) {

        if ( i % 2 === 0 ) {

          newIndices.push( index.getX( i ) );
          newIndices.push( index.getX( i + 1 ) );
          newIndices.push( index.getX( i + 2 ) );


        } else {

          newIndices.push( index.getX( i + 2 ) );
          newIndices.push( index.getX( i + 1 ) );
          newIndices.push( index.getX( i ) );

        }

      }

    }

    if ( ( newIndices.length / 3 ) !== numberOfTriangles ) {

      console.error( 'THREE.GLTFLoader.toTrianglesDrawMode(): Unable to generate correct amount of triangles.' );

    }

    // build final geometry

    var newGeometry = geometry.clone();
    newGeometry.setIndex( newIndices );

    return newGeometry;

  }

  /**
   * Specification: https://github.com/KhronosGroup/glTF/blob/master/specification/2.0/README.md#geometry
   *
   * Creates BufferGeometries from primitives.
   *
   * @param {Array<GLTF.Primitive>} primitives
   * @return {Promise<Array<BufferGeometry>>}
   */
  GLTFParser.prototype.loadGeometries = function ( primitives ) {

    var parser = this;
    var extensions = this.extensions;
    var cache = this.primitiveCache;

    function createDracoPrimitive( primitive ) {

      return extensions[ EXTENSIONS.KHR_DRACO_MESH_COMPRESSION ]
        .decodePrimitive( primitive, parser )
        .then( function ( geometry ) {

          return addPrimitiveAttributes( geometry, primitive, parser );

        } );

    }

    var pending = [];

    for ( var i = 0, il = primitives.length; i < il; i ++ ) {

      var primitive = primitives[ i ];
      var cacheKey = createPrimitiveKey( primitive );

      // See if we've already created this geometry
      var cached = cache[ cacheKey ];

      if ( cached ) {

        // Use the cached geometry if it exists
        pending.push( cached.promise );

      } else {

        var geometryPromise;

        if ( primitive.extensions && primitive.extensions[ EXTENSIONS.KHR_DRACO_MESH_COMPRESSION ] ) {

          // Use DRACO geometry if available
          geometryPromise = createDracoPrimitive( primitive );

        } else {

          // Otherwise create a new geometry
          geometryPromise = addPrimitiveAttributes( new BufferGeometry(), primitive, parser );

        }

        // Cache this geometry
        cache[ cacheKey ] = { primitive: primitive, promise: geometryPromise };

        pending.push( geometryPromise );

      }

    }

    return Promise.all( pending );

  };

  /**
   * Specification: https://github.com/KhronosGroup/glTF/blob/master/specification/2.0/README.md#meshes
   * @param {number} meshIndex
   * @return {Promise<Group|Mesh|SkinnedMesh>}
   */
  GLTFParser.prototype.loadMesh = function ( meshIndex ) {

    var parser = this;
    var json = this.json;

    var meshDef = json.meshes[ meshIndex ];
    var primitives = meshDef.primitives;

    var pending = [];

    for ( var i = 0, il = primitives.length; i < il; i ++ ) {

      var material = primitives[ i ].material === undefined
        ? createDefaultMaterial( this.cache )
        : this.getDependency( 'material', primitives[ i ].material );

      pending.push( material );

    }

    pending.push( parser.loadGeometries( primitives ) );

    return Promise.all( pending ).then( function ( results ) {

      var materials = results.slice( 0, results.length - 1 );
      var geometries = results[ results.length - 1 ];

      var meshes = [];

      for ( var i = 0, il = geometries.length; i < il; i ++ ) {

        var geometry = geometries[ i ];
        var primitive = primitives[ i ];

        // 1. create Mesh

        var mesh;

        var material = materials[ i ];

        if ( primitive.mode === WEBGL_CONSTANTS.TRIANGLES ||
          primitive.mode === WEBGL_CONSTANTS.TRIANGLE_STRIP ||
          primitive.mode === WEBGL_CONSTANTS.TRIANGLE_FAN ||
          primitive.mode === undefined ) {

          // .isSkinnedMesh isn't in glTF spec. See ._markDefs()
          mesh = meshDef.isSkinnedMesh === true
            ? new SkinnedMesh( geometry, material )
            : new Mesh( geometry, material );

          if ( mesh.isSkinnedMesh === true && ! mesh.geometry.attributes.skinWeight.normalized ) {

            // we normalize floating point skin weight array to fix malformed assets (see #15319)
            // it's important to skip this for non-float32 data since normalizeSkinWeights assumes non-normalized inputs
            mesh.normalizeSkinWeights();

          }

          if ( primitive.mode === WEBGL_CONSTANTS.TRIANGLE_STRIP ) {

            mesh.geometry = toTrianglesDrawMode( mesh.geometry, TriangleStripDrawMode );

          } else if ( primitive.mode === WEBGL_CONSTANTS.TRIANGLE_FAN ) {

            mesh.geometry = toTrianglesDrawMode( mesh.geometry, TriangleFanDrawMode );

          }

        } else if ( primitive.mode === WEBGL_CONSTANTS.LINES ) {

          mesh = new LineSegments( geometry, material );

        } else if ( primitive.mode === WEBGL_CONSTANTS.LINE_STRIP ) {

          mesh = new Line( geometry, material );

        } else if ( primitive.mode === WEBGL_CONSTANTS.LINE_LOOP ) {

          mesh = new LineLoop( geometry, material );

        } else if ( primitive.mode === WEBGL_CONSTANTS.POINTS ) {

          mesh = new Points( geometry, material );

        } else {

          throw new Error( 'THREE.GLTFLoader: Primitive mode unsupported: ' + primitive.mode );

        }

        if ( Object.keys( mesh.geometry.morphAttributes ).length > 0 ) {

          updateMorphTargets( mesh, meshDef );

        }

        mesh.name = meshDef.name || ( 'mesh_' + meshIndex );

        if ( geometries.length > 1 ) mesh.name += '_' + i;

        assignExtrasToUserData( mesh, meshDef );

        parser.assignFinalMaterial( mesh );

        meshes.push( mesh );

      }

      if ( meshes.length === 1 ) {

        return meshes[ 0 ];

      }

      var group = new Group();

      for ( var i = 0, il = meshes.length; i < il; i ++ ) {

        group.add( meshes[ i ] );

      }

      return group;

    } );

  };

  /**
   * Specification: https://github.com/KhronosGroup/glTF/tree/master/specification/2.0#cameras
   * @param {number} cameraIndex
   * @return {Promise<THREE.Camera>}
   */
  GLTFParser.prototype.loadCamera = function ( cameraIndex ) {

    var camera;
    var cameraDef = this.json.cameras[ cameraIndex ];
    var params = cameraDef[ cameraDef.type ];

    if ( ! params ) {

      console.warn( 'THREE.GLTFLoader: Missing camera parameters.' );
      return;

    }

    if ( cameraDef.type === 'perspective' ) {

      camera = new PerspectiveCamera( MathUtils.radToDeg( params.yfov ), params.aspectRatio || 1, params.znear || 1, params.zfar || 2e6 );

    } else if ( cameraDef.type === 'orthographic' ) {

      camera = new OrthographicCamera( - params.xmag, params.xmag, params.ymag, - params.ymag, params.znear, params.zfar );

    }

    if ( cameraDef.name ) camera.name = cameraDef.name;

    assignExtrasToUserData( camera, cameraDef );

    return Promise.resolve( camera );

  };

  /**
   * Specification: https://github.com/KhronosGroup/glTF/tree/master/specification/2.0#skins
   * @param {number} skinIndex
   * @return {Promise<Object>}
   */
  GLTFParser.prototype.loadSkin = function ( skinIndex ) {

    var skinDef = this.json.skins[ skinIndex ];

    var skinEntry = { joints: skinDef.joints };

    if ( skinDef.inverseBindMatrices === undefined ) {

      return Promise.resolve( skinEntry );

    }

    return this.getDependency( 'accessor', skinDef.inverseBindMatrices ).then( function ( accessor ) {

      skinEntry.inverseBindMatrices = accessor;

      return skinEntry;

    } );

  };

  /**
   * Specification: https://github.com/KhronosGroup/glTF/tree/master/specification/2.0#animations
   * @param {number} animationIndex
   * @return {Promise<AnimationClip>}
   */
  GLTFParser.prototype.loadAnimation = function ( animationIndex ) {

    var json = this.json;

    var animationDef = json.animations[ animationIndex ];

    var pendingNodes = [];
    var pendingInputAccessors = [];
    var pendingOutputAccessors = [];
    var pendingSamplers = [];
    var pendingTargets = [];

    for ( var i = 0, il = animationDef.channels.length; i < il; i ++ ) {

      var channel = animationDef.channels[ i ];
      var sampler = animationDef.samplers[ channel.sampler ];
      var target = channel.target;
      var name = target.node !== undefined ? target.node : target.id; // NOTE: target.id is deprecated.
      var input = animationDef.parameters !== undefined ? animationDef.parameters[ sampler.input ] : sampler.input;
      var output = animationDef.parameters !== undefined ? animationDef.parameters[ sampler.output ] : sampler.output;

      pendingNodes.push( this.getDependency( 'node', name ) );
      pendingInputAccessors.push( this.getDependency( 'accessor', input ) );
      pendingOutputAccessors.push( this.getDependency( 'accessor', output ) );
      pendingSamplers.push( sampler );
      pendingTargets.push( target );

    }

    return Promise.all( [

      Promise.all( pendingNodes ),
      Promise.all( pendingInputAccessors ),
      Promise.all( pendingOutputAccessors ),
      Promise.all( pendingSamplers ),
      Promise.all( pendingTargets )

    ] ).then( function ( dependencies ) {

      var nodes = dependencies[ 0 ];
      var inputAccessors = dependencies[ 1 ];
      var outputAccessors = dependencies[ 2 ];
      var samplers = dependencies[ 3 ];
      var targets = dependencies[ 4 ];

      var tracks = [];

      for ( var i = 0, il = nodes.length; i < il; i ++ ) {

        var node = nodes[ i ];
        var inputAccessor = inputAccessors[ i ];
        var outputAccessor = outputAccessors[ i ];
        var sampler = samplers[ i ];
        var target = targets[ i ];

        if ( node === undefined ) continue;

        node.updateMatrix();
        node.matrixAutoUpdate = true;

        var TypedKeyframeTrack;

        switch ( PATH_PROPERTIES[ target.path ] ) {

          case PATH_PROPERTIES.weights:

            TypedKeyframeTrack = NumberKeyframeTrack;
            break;

          case PATH_PROPERTIES.rotation:

            TypedKeyframeTrack = QuaternionKeyframeTrack;
            break;

          case PATH_PROPERTIES.position:
          case PATH_PROPERTIES.scale:
          default:

            TypedKeyframeTrack = VectorKeyframeTrack;
            break;

        }

        var targetName = node.name ? node.name : node.uuid;

        var interpolation = sampler.interpolation !== undefined ? INTERPOLATION[ sampler.interpolation ] : InterpolateLinear;

        var targetNames = [];

        if ( PATH_PROPERTIES[ target.path ] === PATH_PROPERTIES.weights ) {

          // Node may be a Group (glTF mesh with several primitives) or a Mesh.
          node.traverse( function ( object ) {

            if ( object.isMesh === true && object.morphTargetInfluences ) {

              targetNames.push( object.name ? object.name : object.uuid );

            }

          } );

        } else {

          targetNames.push( targetName );

        }

        var outputArray = outputAccessor.array;

        if ( outputAccessor.normalized ) {

          var scale;

          if ( outputArray.constructor === Int8Array ) {

            scale = 1 / 127;

          } else if ( outputArray.constructor === Uint8Array ) {

            scale = 1 / 255;

          } else if ( outputArray.constructor == Int16Array ) {

            scale = 1 / 32767;

          } else if ( outputArray.constructor === Uint16Array ) {

            scale = 1 / 65535;

          } else {

            throw new Error( 'THREE.GLTFLoader: Unsupported output accessor component type.' );

          }

          var scaled = new Float32Array( outputArray.length );

          for ( var j = 0, jl = outputArray.length; j < jl; j ++ ) {

            scaled[ j ] = outputArray[ j ] * scale;

          }

          outputArray = scaled;

        }

        for ( var j = 0, jl = targetNames.length; j < jl; j ++ ) {

          var track = new TypedKeyframeTrack(
            targetNames[ j ] + '.' + PATH_PROPERTIES[ target.path ],
            inputAccessor.array,
            outputArray,
            interpolation
          );

          // Override interpolation with custom factory method.
          if ( sampler.interpolation === 'CUBICSPLINE' ) {

            track.createInterpolant = function InterpolantFactoryMethodGLTFCubicSpline( result ) {

              // A CUBICSPLINE keyframe in glTF has three output values for each input value,
              // representing inTangent, splineVertex, and outTangent. As a result, track.getValueSize()
              // must be divided by three to get the interpolant's sampleSize argument.

              return new GLTFCubicSplineInterpolant( this.times, this.values, this.getValueSize() / 3, result );

            };

            // Mark as CUBICSPLINE. `track.getInterpolation()` doesn't support custom interpolants.
            track.createInterpolant.isInterpolantFactoryMethodGLTFCubicSpline = true;

          }

          tracks.push( track );

        }

      }

      var name = animationDef.name ? animationDef.name : 'animation_' + animationIndex;

      return new AnimationClip( name, undefined, tracks );

    } );

  };

  /**
   * Specification: https://github.com/KhronosGroup/glTF/tree/master/specification/2.0#nodes-and-hierarchy
   * @param {number} nodeIndex
   * @return {Promise<Object3D>}
   */
  GLTFParser.prototype.loadNode = function ( nodeIndex ) {

    var json = this.json;
    var extensions = this.extensions;
    var parser = this;

    var nodeDef = json.nodes[ nodeIndex ];

    return ( function () {

      var pending = [];

      if ( nodeDef.mesh !== undefined ) {

        pending.push( parser.getDependency( 'mesh', nodeDef.mesh ).then( function ( mesh ) {

          var node = parser._getNodeRef( parser.meshCache, nodeDef.mesh, mesh );

          // if weights are provided on the node, override weights on the mesh.
          if ( nodeDef.weights !== undefined ) {

            node.traverse( function ( o ) {

              if ( ! o.isMesh ) return;

              for ( var i = 0, il = nodeDef.weights.length; i < il; i ++ ) {

                o.morphTargetInfluences[ i ] = nodeDef.weights[ i ];

              }

            } );

          }

          return node;

        } ) );

      }

      if ( nodeDef.camera !== undefined ) {

        pending.push( parser.getDependency( 'camera', nodeDef.camera ).then( function ( camera ) {

          return parser._getNodeRef( parser.cameraCache, nodeDef.camera, camera );

        } ) );

      }

      if ( nodeDef.extensions
        && nodeDef.extensions[ EXTENSIONS.KHR_LIGHTS_PUNCTUAL ]
        && nodeDef.extensions[ EXTENSIONS.KHR_LIGHTS_PUNCTUAL ].light !== undefined ) {

        var lightIndex = nodeDef.extensions[ EXTENSIONS.KHR_LIGHTS_PUNCTUAL ].light;

        pending.push( parser.getDependency( 'light', lightIndex ).then( function ( light ) {

          return parser._getNodeRef( parser.lightCache, lightIndex, light );

        } ) );

      }

      return Promise.all( pending );

    }() ).then( function ( objects ) {

      var node;

      // .isBone isn't in glTF spec. See ._markDefs
      if ( nodeDef.isBone === true ) {

        node = new Bone();

      } else if ( objects.length > 1 ) {

        node = new Group();

      } else if ( objects.length === 1 ) {

        node = objects[ 0 ];

      } else {

        node = new Object3D();

      }

      if ( node !== objects[ 0 ] ) {

        for ( var i = 0, il = objects.length; i < il; i ++ ) {

          node.add( objects[ i ] );

        }

      }

      if ( nodeDef.name ) {

        node.userData.name = nodeDef.name;
        node.name = PropertyBinding.sanitizeNodeName( nodeDef.name );

      }

      assignExtrasToUserData( node, nodeDef );

      if ( nodeDef.extensions ) addUnknownExtensionsToUserData( extensions, node, nodeDef );

      if ( nodeDef.matrix !== undefined ) {

        var matrix = new Matrix4();
        matrix.fromArray( nodeDef.matrix );
        node.applyMatrix4( matrix );

      } else {

        if ( nodeDef.translation !== undefined ) {

          node.position.fromArray( nodeDef.translation );

        }

        if ( nodeDef.rotation !== undefined ) {

          node.quaternion.fromArray( nodeDef.rotation );

        }

        if ( nodeDef.scale !== undefined ) {

          node.scale.fromArray( nodeDef.scale );

        }

      }

      parser.associations.set( node, { type: 'nodes', index: nodeIndex } );

      return node;

    } );

  };

  /**
   * Specification: https://github.com/KhronosGroup/glTF/tree/master/specification/2.0#scenes
   * @param {number} sceneIndex
   * @return {Promise<Group>}
   */
  GLTFParser.prototype.loadScene = function () {

    // scene node hierachy builder

    function buildNodeHierachy( nodeId, parentObject, json, parser ) {

      var nodeDef = json.nodes[ nodeId ];

      return parser.getDependency( 'node', nodeId ).then( function ( node ) {

        if ( nodeDef.skin === undefined ) return node;

        // build skeleton here as well

        var skinEntry;

        return parser.getDependency( 'skin', nodeDef.skin ).then( function ( skin ) {

          skinEntry = skin;

          var pendingJoints = [];

          for ( var i = 0, il = skinEntry.joints.length; i < il; i ++ ) {

            pendingJoints.push( parser.getDependency( 'node', skinEntry.joints[ i ] ) );

          }

          return Promise.all( pendingJoints );

        } ).then( function ( jointNodes ) {

          node.traverse( function ( mesh ) {

            if ( ! mesh.isMesh ) return;

            var bones = [];
            var boneInverses = [];

            for ( var j = 0, jl = jointNodes.length; j < jl; j ++ ) {

              var jointNode = jointNodes[ j ];

              if ( jointNode ) {

                bones.push( jointNode );

                var mat = new Matrix4();

                if ( skinEntry.inverseBindMatrices !== undefined ) {

                  mat.fromArray( skinEntry.inverseBindMatrices.array, j * 16 );

                }

                boneInverses.push( mat );

              } else {

                console.warn( 'THREE.GLTFLoader: Joint "%s" could not be found.', skinEntry.joints[ j ] );

              }

            }

            mesh.bind( new Skeleton( bones, boneInverses ), mesh.matrixWorld );

          } );

          return node;

        } );

      } ).then( function ( node ) {

        // build node hierachy

        parentObject.add( node );

        var pending = [];

        if ( nodeDef.children ) {

          var children = nodeDef.children;

          for ( var i = 0, il = children.length; i < il; i ++ ) {

            var child = children[ i ];
            pending.push( buildNodeHierachy( child, node, json, parser ) );

          }

        }

        return Promise.all( pending );

      } );

    }

    return function loadScene( sceneIndex ) {

      var json = this.json;
      var extensions = this.extensions;
      var sceneDef = this.json.scenes[ sceneIndex ];
      var parser = this;

      // Loader returns Group, not Scene.
      // See: https://github.com/mrdoob/three.js/issues/18342#issuecomment-578981172
      var scene = new Group();
      if ( sceneDef.name ) scene.name = sceneDef.name;

      assignExtrasToUserData( scene, sceneDef );

      if ( sceneDef.extensions ) addUnknownExtensionsToUserData( extensions, scene, sceneDef );

      var nodeIds = sceneDef.nodes || [];

      var pending = [];

      for ( var i = 0, il = nodeIds.length; i < il; i ++ ) {

        pending.push( buildNodeHierachy( nodeIds[ i ], scene, json, parser ) );

      }

      return Promise.all( pending ).then( function () {

        return scene;

      } );

    };

  }();

  return GLTFLoader;

} )();

export { GLTFLoader };
